As you will see from my sig, I have 3, W123 300D's.
In the youngest, the '84, if I am descending a hill and I shift back to 3rd, I hear the engine RPM rise and I feel the retardation of the engine braking.
On the other 2, when I shift down to 3rd, there is no noticable (audible) increase in engine RPM (no tacho), but I do get some retardation. I have not quantified the differences in vehicle speed on the same hill, but plan on doing so today.
All vehicles drive normally with no flaring during shifts, although they all snatch 1-2 & 2-3 when cold. They all have the same diff ratio.
Is there a problem with the transmission?

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.